Thanks for posting your downtime here. Does these 5xx errors correspond with App Engine
incident #16002? For this to be true, the runtimes would have to have been Java or Go and the 5xx errors mostly between
2016-02-03 18:38 PST and
2016-02-03 18:57 PST.
If this is not the case, please provide more details about runtimes, module configuration, time frames, logs, code snippets, etc. so that we may further investigate this issue. If it can be reproduced, the Google App Engine public issue tracker may be a better forum with which to provide steps for reproduction.